Many communication systems, such as wireless communication systems, require an accurate timebase for satisfactory operation. For example, a code division multiple access (CDMA) wireless communication system comprises a plurality of base stations, each of which is typically positioned in a fixed location and requires an accurate timebase for satisfactory operation. The operation of a CDMA system and the requirement for an accurate timebase are known in the art and need not be described in greater detail herein.
It is known to use a global positioning system (GPS) array of satellites to provide an accurate timebase for such communication systems. Each base station is equipped with a sophisticated GPS antenna and receiver (not shown) to communicate with multiple satellites of the GPS. Based on synchronized communication with a number of satellites of the GPS, the GPS receiver provides the base station with a highly accurate timebase that may be used in subsequent communications between the base station and other base stations and between the base station and one or more mobile units.
The aforementioned GPS requires a sophisticated receiver and antenna system to assure adequate communications with multiple satellites. In an ideal implementation, the GPS antenna is mounted in a location that is free from obstructions, such as natural terrain (e.g., mountains) or man-made structures (e.g., buildings). If the base station is located in an area where communication links with the satellites are disrupted by terrain or man-made structures, it may not be possible to provide the base station with an accurate timebase. Therefore, it can be appreciated that there is a significant need for a technique to provide accurate timebase in circumstances where the GPS cannot be used to provide the desired degree of accuracy. The present invention provides this, and other advantages, as will be apparent from the following detailed description and accompanying figures.